<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>使用WebGL绘制一个点</title>
</head>

<body>
  <!--canvas标签创建一个宽高均为500像素，背景为蓝色的矩形画布-->
  <canvas id="webgl" width="500" height="500" style="background-color: blue"></canvas>

</body>
<!-- 顶点着色器源码 -->
<script id="vertexShader" type="x-shader/x-vertex">

  void main() {
    //给内置变量gl_PointSize赋值像素大小
    gl_PointSize=20.0;
    //顶点位置，位于坐标原点
    gl_Position =vec4(0.0,0.0,0.0,1.0);
  }

</script>
<!-- 片元着色器源码 -->
<script id="fragmentShader" type="x-shader/x-fragment">

  void main() {
    gl_FragColor = vec4(1.0,0.0,0.0,1.0);
  }

</script>

<script>
  //通过getElementById()方法获取canvas画布
  var canvas = document.getElementById('webgl');
  //通过方法getContext()获取WebGL上下文
  var gl = canvas.getContext('webgl');

  //顶点着色器源码
  var vertexShaderSource = document.getElementById('vertexShader').innerText;

  //片元着色器源码
  var fragShaderSource = document.getElementById('fragmentShader').innerText;

  //初始化着色器
  var program = initShader(gl, vertexShaderSource, fragShaderSource);
  //开始绘制，显示器显示结果
  gl.drawArrays(gl.POINTS, 0, 1);

  //声明初始化着色器函数
  function initShader(gl, vertexShaderSource, fragmentShaderSource) {
    //创建顶点着色器对象
    var vertexShader = gl.createShader(gl.VERTEX_SHADER);
    //创建片元着色器对象
    var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
    //引入顶点、片元着色器源代码
    gl.shaderSource(vertexShader, vertexShaderSource);
    gl.shaderSource(fragmentShader, fragmentShaderSource);
    //编译顶点、片元着色器
    gl.compileShader(vertexShader);
    gl.compileShader(fragmentShader);

    //创建程序对象program
    var program = gl.createProgram();
    //附着顶点着色器和片元着色器到program
    gl.attachShader(program, vertexShader);
    gl.attachShader(program, fragmentShader);
    //链接program
    gl.linkProgram(program);
    //使用program
    gl.useProgram(program);
    //返回程序program对象
    return program;
  }
</script>

</html>